This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Inhibitors of apoptosis (IAPs) are multi-domain anti-apoptotic factors that can block cell death. IAP family members contain a C-terminal RING domain with E3 ubiquitin ligase activity. Binding of small molecule antagonists to IAP repeats within cellular IAPs (cIAPs) promotes cIAP auto- ubiquitination and proteasomal degradation, thereby releasing cIAP inhibition of apoptosis. Small molecule binding remote from the RING domain induces ligase activity, and a conformational change we want to understand. We seek SAXS data from cIAP1 both in the absence and presence of small molecule antagonists.